Method and apparatus for transmitting multimedia broadcast data in wireless communication system

ABSTRACT

A base station and method for use in a wireless system are provided. The method includes receiving, by a base station, one or more service data unit (SDUs) from a core network node; receiving, by the base station, a control message including respective length information of the one or more SDUs from the core network node; and processing, by the base station, the one or more SDUs, based on the length information included in the control message. The control message is transmitted after the one or more SDUs are transmitted from the core network node.

PRIORITY

This application is a Continuation Application of U.S. application Ser.No. 14/579,026, which was filed in the U.S. Patent and Trademark Officeon Dec. 22, 2014, which is a Continuation Application of U.S.application Ser. No. 13/379,252, issued as U.S. Pat. No. 8,923,345,which was filed in the U.S. Patent and Trademark Office on Dec. 19,2011, as a National Stage Entry of PCT/KR2010/003907, which was filed onJun. 17, 2010, and claims priority to Korean Patent Application No.10-2009-0053850, which was filed in the Korean Intellectual PropertyOffice on Jun. 17, 2009, the content of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system and, inparticular, to a method and apparatus for generating and transmittingmultimedia broadcast data in a wireless communication system.

2. Description of the Related Art

Mobile communication systems have been developed to provide thesubscribers with voice communication services on the move. With therapid advance of technologies, the mobile communication systems haveevolved to support high speed data communication services as well as thestandard voice communication services.

Recently, as the next generation mobile communication system of the3^(rd) Generation Partnership Project (3GPP), Long Term Evolution (LTE)is under development. The LTE system is a technology for realizinghigh-speed packet-based communication at about 100 Mbps, aiming atcommercialization in around 2010. Regarding the commercialization of theLTE system, a discussion is being held on several schemes: one schemefor reducing the number of nodes located in a communication path bysimplifying a configuration of the network, and another scheme formaximally approximating wireless protocols to wireless channels.

Unlike voice service, data service is characterized in that the resourceis allocated according to the data amount to be transmitted and channelcondition. Accordingly, in the wireless communication system such ascellular communication system, a scheduler manages resource allocationin consideration of the resource amount, channel condition, and dataamount. This is also the case in the LTE system as one of the nextgeneration mobile communication systems such that the scheduler locatedin the base station manages and allocates the radio resource. Also, thesecond layer protocols such as MAC and RLC are supported in the basestation.

The wireless communication system such as LTE system supporting highspeed high quality service meets the requirements for providingmultimedia broadcast service, and thus there are many researches beingconducted to provide the multimedia broadcast service in the wirelesscommunication system. The multimedia broadcast service supported in LTEis called Multimedia Broadcast Multicast Service (MBMS) which isprovided in such a manner that a plurality of base stations transmit thesame broadcast data generated by an MBMS server. In case that multiplebase stations transmit the same data, the transmission efficiency on theradio channel increases significantly. As aforementioned, however, sincethe second layer protocols such as the Media Access Control (MAC) andRadio Link Control (RLC) are placed at the base station, the datagenerated by the MBMS server are likely to lose data integrity throughthe second layer process at different base stations.

SUMMARY

Accordingly, the present invention is designed to address at least theproblems and/or disadvantages described above and to provide at leastthe advantages described below.

It is an aspect of the prevent invention to provide a method andapparatus for transmitting multimedia broadcast data over radio channelwhile maintaining data integrity.

In accordance with an aspect of the present invention, a method is[provided for use in a wireless communication system. The methodincludes receiving, by a base station, one or more service data unit(SDUs) from a core network node; receiving, by the base station, acontrol message including respective length information of the one ormore SDUs from the core network node; and processing, by the basestation, the one or more SDUs, based on the length information includedin the control message. The control message is transmitted after the oneor more SDUs are transmitted from the core network node.

In accordance with another aspect of the present invention, a basestation is provided for use in a wireless communication system. The basestation includes a transceiver configured to transmit and receive asignal; and a controller configured to control to receive one or moreservice data unit (SDUs) from a core network node, to receive a controlmessage including respective length information of the one or more SDUsfrom the core network node, and to process the one or more SDUs, basedon the length information included in the control message. The controlmessage is transmitted after the one or more SDUs are transmitted fromthe core network node.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a configuration of an LTE mobilecommunication system;

FIG. 2 is a diagram illustrating a protocol stack of an LTE mobilecommunication system;

FIG. 3 is a diagram illustrating a method for providing a normal MBMSservice;

FIG. 4 is a diagram illustrating an operation of a legacy eNB inreception of a part of MBMS data;

FIG. 5 is a diagram illustrating a configuration of a normal SYNC frame;

FIG. 6 is a diagram illustrating a normal principle of configuring PNand OC in the SYNC frame;

FIG. 7 is a diagram illustrating a normal principle of determining thedata amount and number of missed data based on PN and OC;

FIG. 8 is a diagram illustrating the first embodiment of the presentinvention;

FIG. 9 is a diagram illustrating the first embodiment of the presentinvention;

FIG. 10 is a flowchart illustrating an eNB procedure according to thefirst embodiment of the present invention;

FIG. 11 is a diagram illustrating the second embodiment of the presentinvention;

FIG. 12 is a diagram illustrating a configuration of SYNC frameaccording to the second embodiment of the present invention;

FIG. 13 is flowchart illustrating an eNB procedure according to thesecond embodiment of the present invention;

FIG. 14 is a drawing illustrating the third embodiment of the presentinvention.

FIG. 15 is a flowchart illustrating an eNB device operation according tothe third embodiment of the present invention; and

FIG. 16 is a block diagram illustrating the eNB device according to anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

The terms and words used in this description and the appended claims arenot to be interpreted in common or lexical meaning but, based on theprinciple that an inventor can adequately define the meanings of termsto best describe the invention, to be interpreted in the meaning andconcept conforming to the technical concept of the present invention.

Prior to the start of explanation on the present invention, adescription is made of an LTE mobile communication system with referenceto FIGS. 1 and 2.

FIG. 1 is a diagram illustrating a configuration of an LTE mobilecommunication system.

Referring to FIG. 1, the LTE mobile communication system includesEvolved Radio Access Network (hereinafter, referred to as E-RAN) 110 and112) is simplified in two-node structure of evolved Node B (hereinafter,referred to as eNB or Node B) 120, 122, 124, 126, and 128 and highernode (Access Gateway or enhance Gateway GPRS Support Node, hereinafterreferred to as EGGSN) 130 and 132. The User Equipment (hereinafter,referred to as UE) 101 accesses Internet Protocol (IP) network 114 viaE-RANs 110 and 112.

The eNBs 120 to 128 corresponds to legacy node B of UMTS system. TheeNBs 120 to 128 are connected with the UE 101 via radio channel andresponsible for more complex functions as compared to the legacy node B.Since all the user traffics including real time services such as Voiceover IP (VoIP) are transmitted through shared channel, there is a needof a device for scheduling the based on the state information of the UEs101, and the eNB is responsible for this function in LTE. Each of theeNBs 120 to 128 manages a plurality cells.

In order to meet the requirements of maximum data rate of 100 Mbps, LTEadopts Orthogonal Frequency Division Multiplexing (OFDM) as radio accesstechnology in maximum 20 MHz bandwidth. LTE also adopts AdaptiveModulation & Coding (AMC) for determining modulation scheme and channelcoding rate depending on the channel condition of the UE 101.

Although not depicted in FIG. 1, the LTE system includes an MBMS serverwhich generates MBMS (Multimedia Broadcast Multicast Server) data to theeNBs 120 to 128. The MBMS server and eNBs 120 to 128 are connected toeach other through an IP network.

FIG. 2 is a diagram illustrating a protocol stack of an LTE mobilecommunication system.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, and Medium Access Control (MAC) 215 and 230.

The PDCP 205 and 240 is responsible for IP headercompression/decompression, and the RLC 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation. An RLCheader is added at the RLC layer 210 and 235 for the ARQ operation.

The MAC 215 and 230 is responsible for establishing connection to aplurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUsand demultiplex the MAC PDUs into RLC PDUs. A MAC header is added at theMAC layer 215 and 230 for multiplexing and demultiplexing operations.

The PHY 220 and 225 performs channel coding on the MAC PDU and modulatesthe MAC PDU into OFDM symbols to transmit over radio channel or performsdemodulating and channel-decoding on the received OFDM symbols anddelivers the decoded data to the higher layer. In view of transmission,the data input to a protocol entity is referred to as Service Data unit(SDU), and the data output from the protocol entity is referred to asProtocol Data Unit (PDU).

A description is made of the MBMS (Multimedia Broadcast MulticastService) hereinafter.

FIG. 3 is a diagram illustrating a method for providing a normal MBMSservice.

Referring to FIG. 3, the MBMS server 305 generates MBMS service data tothe eNBs 310, 315, 320, 325, and 330 participated in the MBMStransmission. The eNBs 310, 315, 320, 325, and 330 store the datareceived from MBMS server 305 and transmit the stored data at apredetermined timing simultaneously.

Since the data are transmitted at the same time, the signal is amplifiedin strength and thus the UEs located in the coverage of the eNBs 310,315, 32, 325, and 330 receive the signal from the multiple eNBs 310,315, 320, 325, and 330 so as to experience high reception quality ascompared to the case when receiving the signal from only one eNB. Inorder for the multiple eNBs 310, 315, 320, 325, and 330 to transmit thesame signal, it is required to fulfill the following conditions.

Firstly, the eNBs 310, 315, 320, 325, and 330 must receive the samedata; secondly, the eNBs 310, 315, 320, 325, and 330 must process thereceived data into the same data; and finally, the eNBs 310, 315, 320,325, and 330 must transmit the same data simultaneously.

FIG. 4 is a diagram illustrating an operation of a legacy eNB inreception of a part of MBMS data.

Referring to FIG. 4, the MBMS server transmits RLC SDU generated througha PDCP process on IP packet to eNBs, in general. Since headercompression and decompression which is usual in normal data is notapplied to MBMS data, RLC SDU is maintained in the form of the IPpacket. Although the description is directed to the case whether the eNBreceives RLC SDU, this is identical to the case that the eNB receivesthe IP packet.

The eNB segments or concatenates the RLC SDUs received from the MBMSserver into RLC PDUs of appropriated size with the addition of RLCheader and then multiplexes the RLC PDUs and adds MAC head to generateMAC PDUs. The MAC PDUs are transmitted on the radio channel. in moredetail, since only one RLC PDU is encapsulated in a MAC PDU, the MAC PDUis generated by segmenting an RLC SDU or combining multiple RLC SDUs andthen adding RLC header 415 and MAC header 410 to each RLC SDU.

Since all of the eNBs have the RLC and MAC protocols, if the RLC SDUsare received by the eNBs without loss, the MAC PDUs which the respectiveeNBs have generated with the RLC SDUs are identical among each other.However, there is any RLC SDU missed by an eNB, the eNB fails togenerate the MAC PDU due to the missed RLC SDU.

The best approach to solve this problem is to transmit the next MAC PDUfollowing the MAC PDU including the missed RLC SDU. For example, if aneNB has received the RLC SDUs with the exception of RLC SDU [m+1] 425,the eNB suspends the MAC PDUs including the RLC SDU [m+1] a bit, i.e.MAC PDU [n] 420 and MAC PDU [n+1] 425, and transmits the MAC PDU [n+2]430.

Meanwhile, in order for the eNB to transmit MAC PDU [n+2] first, the eNBhas to check which RLC SDUs start at which bytes. Here, if it ispossible to predict the overheads of MAC and RLC headers added to eachRLC SDU, the eNB can calculate the bytes occupied by the missed RLC SDUsin MAC PDUs from a number of missed RLC SDUs and sum of the sizes ofmissed RLC SDUs. Using this information, the eNB also can determine theRLC SDUs included in the suspended MAC PDUs and the bytes occupied bythe RLC SDUs in the MAC PDU to be transmitted.

If it is possible to predict the RLC overhead and MAC overhead amountcaused by one RLC SDU, the information necessary for the eNB to performthe aforementioned operation is the sum of the sizes of missed RLC SDUsand the number of missed RLC SDUs. Accordingly, the MBMS servertransmits the RLC SDUs in SYNC frame to notify the eNB of the sum of thesizes of missed RLC SDUs and the number of missed RLC SDUs.

FIG. 5 is a diagram illustrating a configuration of a normal SYNC frame.

Referring to FIG. 5, the SYNC frame 505 includes a header 510 and apayload 520, and the payload 520 includes one RLC SDU. In order tosimplify the explanation, the term RLC SDU is used interchangeably withthe data included in the payload 520 of the SYNC frame 505.

The header 510 includes packet number, octet counter, and SYNCperiod-related information. The Packet Number (PN) in the informationindicating the index of the SYNC frame, the Octet Counter (OC) is theinformation indicating the total amount of the payload of the SYNCframes transmitted before the corresponding SYNC frame. The SYNCperiod-related information in the information indicating the period forwhich the RLC SDU is transmitted in the SYNC frame. Here, the SYNCperiod is the period defined on a radio channel.

One or more subframes are designated as MBMS subframes for one SYNCperiod, and each MBMS subframe carries the MAC PDUs containing only MBMSdata. The MBMS data amount to be transmitted curing the correspondingSYNC period is determined depending on the number of MBMS subframesallocated for the SYNC period. Also, the network determines the numberof MBMS subframes for the SYNC period in consideration of the data rateof the MBMS service.

Meanwhile, in order to maintain PN and OC to appropriate levels, theMBMS server manages PN and OC by referencing the SYNC period. Forexample, the MBMS server transmits the SYNC frames carrying the dataamount corresponding to the SYNC period and then initializes the PN andOC of the SYNC protocol to 0. The MBMS server repeats increment of thePN and OC for the transmission of SYNC frames as much as the data amountcorresponding to the next SYNC period and initialization of the PN andOC to 0 during the next SYNC period.

FIG. 6 is a diagram illustrating a normal principle of configuring PNand OC in the SYNC frame.

Referring to FIG. 6, if the data amount to be transmitted for SYNCperiod is 700 bytes, the MBMS server transmits 7 SYNC frames from theSYNC frame 610 to the SYNC frame 635 containing 700 bytes for a certainSYNC period. Both the PN and OC of the first SYNC frame 610 are set to0, and the PN and OC of the fifth SYNC frame 630 are set to 4 and 500respectively. Since the next SYNC frame 640 is transmitted in a new SYNCperiod, the PN and OC are initialized to 0. For reference, the dataamount transmitted for one SYNC period is constant in general. Forsimplicity purpose, the RLC and MAC headers are not taken into account.

The eNB can calculate the number of missed SYNC frames and the sum ofthe sizes of the RLC SDUs constituting the SYNC frames based on PN andOC.

FIG. 7 is a diagram illustrating a normal principle of determining thedata amount and number of missed data based on PN and OC.

Referring to FIG. 7, if the SYNC frames 705 and 710 are not received,the eNB determines the three missed SYNC frames and the total 400 bytesof missed data using PN and OC of the SYNC frames 705 and 710.

Assuming that the RLC/MAC overhead per RLC SDU is 4 bytes, the eNB cancheck that the total 412 bytes corresponding to the missed RLC SDUsshould be contained in the MAC PDU. For example, if 50 bytes of MAC PDU[n] are occupied by the RLC SDU 705 already and if the 412 bytesinserted in the rest 450 bytes, 38 bytes are remained empty. In thiscase, the first 38 bytes of the RLC SDU 710 occupy the remained spacesuch that the MAC PDU [n+1] is filled with from the 39^(th) byte of theRLC SDU 710. Accordingly, the eNB suspends the MAC PDU [n] carrying themissed RLC SDU and transmits the MAC PDU [n+1] which is configurednormally.

As aforementioned, in order to determine the MAC PDU to be transmittedand the RLC SDU and its start byte to be filled in the MAC PDU, it mustbe possible to estimate the sizes of the RLC and MAC overheads per RLCSDU. In the current RLC and MAC protocols, however, the RLC/MAC overheadcan vary in size according to how the RLC SDU are encapsulated in RLCPDU and whether the RLC PDU is greater than a predetermined value. Forexample, in case that the last byte of the RLC SDU to be encapsulated inan RLC PDU matches with the last byte of the RLC PDU, an RLC field, socalled LI (Length Indicator), is omitted.

Also, the overhead caused by LI also can vary according to the number ofLIs included in the RLC PDU. The overhead caused by one LI is 2 bytes,but the overhead increases to 3 bytes for two LIs. In order to make thesize of the RLC/MAC overhead per RLC SDU predictable, it is necessary tomodify the RLC and MAC standards. However, if it is taken intoconsideration that the RLC and MAC protocols should work with the UEsnot supporting MBMS, protocol modification is not preferred.

In order to solve this problem, the present invention proposes a methodand apparatus for the eNBs to configure and transmit MAC PDUs for MBMSwithout modification of the RLC and MAC protocols.

First Embodiment

In the first embodiment of the present invention, if a series of SYNCframes are not received, the eNB calculates the size of RLC SDU filledin the SYNC frame using the PN and OC values of the SYNC frame anddetermines the MAC PDUs to be transmitted or not and the start byte ofthe RLC SDU that is to be carried in the MAC PDU.

If it is detected that a series of SYNC frames are not received in acertain SYNC period, the eNB stops building MAC PDU from the SYNC framesincluding and following the missed SYNC frames. That is, the MBMStransmission is suspended for the duration reserved for the MAC PDUsthat are not built.

In case that the size of the missed RLC SDU is recognized, the eNB candetermine the RLC PDU carrying the corresponding RLC SDU and the numberof bytes of the overhead of the RLC PDU. In the current SYNC protocol,however, it is impossible to calculate the size of the RLC SDU when aseries of missed SYNC frames and the number of bytes of the overhead ofthe RLC SDUs although it possible when only one SYNC frame is missed.Accordingly, when a series of SYNC frames are missed, the eNB stopstransmitting MAC PDU, initializing PN and OC to 0, and restartstransmitting MAC PDU from the start time point of the next SYNC periodfor which the MAC PDU is built with from the first RLC SDU.

FIG. 8 is a diagram illustrating the first embodiment of the presentinvention. Particularly, FIG. 1 shows the eNB operation in case where aseries of SYNC frames are not received.

Referring to FIG. 8, the RLC SDUs are received successfully with theexception of the RLC PDU 820 in a certain SYNC period among 5 RLC SDUs810 to 850. The eNBs processes the successfully received RLC SDUsaccording to the conventional RLC and MAC protocols to build RLC PDU andMAC PDU and transmits the MAC PDU 865 in an MBMS subframe.

The size of the missed RLC SDU 820 is calculated using PN and OC of thesynch frame, and it continues to build RLC PDU and MAC PDU as if thecorresponding size of RLC SDU is received. This can be implemented invarious manner, e.g. by generating a virtual RLC SDU equal to the missedRLC SDU in size and building RLC PDU and MAC PDU continuously with thegenerated RLC SDU. In spite of the missed RLC SDU, the MAC PDU 870including the virtually generated RLC SDU is discarded rather thantransmitted in the corresponding MBMS subframe.

This means that the MAC PDU is not transmitted in the MBMS subframe. TheeNB restarts transmission from the MAC PDU which is not influenced bythe missed RLC SDU, i.e. the MAC PDU 875 containing the RLC SDU, in theMBMS subframe. In more detail, when it is possible to calculate the sizeof the RLC SDU contained in the missed SYNC frame, the eNB can continuebuilding RLC PDU and MAC PDU in consideration of the size of the missedRLC SDU, and transmitting MAC PDUs having no missed RLC SDU in the MBMSsubframe while skipping transmission of the MAC PDU in the MBMS subframereserved for transmitting the MAC PDUs containing the missed RLC SDUs.

FIG. 9 is a diagram illustrating the first embodiment of the presentinvention. Particularly, FIG. 9 shows the eNB operation in case that oneor more RLC SDUs are not received in series.

Referring to FIG. 9, RLC SDUs 920 and 925 are not received among thefive RLC SDUs 910 to 930 in a SYNC period. The eNB processes thesuccessfully received RLC SDUs 910 and 915 using the conventional RLCand MAC protocols to build RLC PDUs 945 and 965 and transmits the MACPDU 965 in a subframe. The eNB analyzes the PNs and OCs of RLC SDUs 915and 930 to check that the two RLC SDUs are missed in series andcalculate the sum of the sizes of the missed RLC SDUs.

In case that more than one RLC SDU are not received in series, the eNBcannot check the sizes of individual missed RLC SDUs and thus failscalculating the space occupied by the missed RLC SDUs in MAC PDU and, asa sequence, it is impossible to configure the MAC PDU precisely in spiteof the successful receipt of the next RLC SDUs. Accordingly, when it isdetected that multiple RLC SDUs are not received, the eNB suspendsbuilding MAC PDU until the next SYNC period starts. Also, thetransmission of the MAC PDUs scheduled to be transmitted in the MBMSsubframe but not configured is canceled. If the next SYNC period starts,the eNB restarts MBMS data transmission.

FIG. 10 is a flowchart illustrating an eNB procedure according to thefirst embodiment of the present invention.

Referring to FIG. 10, once a SYNC period starts at step 1005, the eNBstarts operation for generating the MAC PDU to be transmitted in thefirst MBMS subframe for which no MAC PDU is configured among the MBMSsubframes assigned for the SYNC period at step 1010. The eNB segments orconcatenates RLC SDUs that have not been encapsulated in MAC PDU or someof the RLC SDUs in match with the size of the RLC PDU.

Next, the eNB determines whether there is any missed RLC SDU until thepayload of the RLC PDU is filled entirely at step 1015. If the RLC PDUis filled entirely without missed RLC SDU, the procedure goes to step1020 and, otherwise if any missed RLC SDU is detected until the payloadof the RLC PDU is filled entirely, step 1030. If there is any missed RLCSDU at step 1015, this means that the PNs of the two consecutive RLCSDUs are not in series.

The eNB configures an RLC PDU by adding a header to the RLC payloadgenerated by segmenting/combining the RLC SDUs and multiplexes RLC PDUsinto a MAC PDU at step 1020. Next, the eNB transmits the MAC PDU in thecorresponding MBMS subframe at step 1025, and then the procedure goes tostep 1055.

If any missed RLC SDU is detected before filling the RLC PDU entirely,the eNB determines whether a number of missed RLC SDUs is greater thanone and, if so, missed in series at step 1030. This can be determined bychecking the PNs of the RLC SDUs adjacent to the missed RLC SDUs. If thenumber of missed RLC SDUs is one at step 1030, the procedure goes tostep 1035.

The eNB calculates the size of the missed RLC SDU using OCs of the RLCSDUs adjacent to the missed RLC SDU and determines the MAC PDUcorresponding to the MBMS in which the missed RLC SDU is scheduled inconsideration of the size of the missed RLC SDU at step 1035. This alsocan be determined by performing a MAC PDU creation process with thegeneration of a virtual RLC SDU having the same size as the missed RLCSDU and checking the MAC PDU in which the RLC SDU equal in size to themissed RLC SDU is encapsulated. The eNB stops transmitting the MAC PDUreserved to carry the missed RLC SDU in the MBMS subframe at step 1040and transmits the first MAC PDU configured with the encapsulation of thevalid RLC SDUs in the corresponding MBMS subframe at step 1045. Forexample, it is possible to perform the normal MAC PDU generation processwith the creasing of virtual RLC SDU equal to the missed RLC SDU in sizeuntil the first MAC PDU encapsulating the RLC SDU equal in size to themissed RLC SDU is generated.

If it is determined that more than one RLC SDU are missed in series atstep 1030, the eNB transmits the MAC PDUs generated until then in thecorresponding MBMS subframe and stops generations of more MAC PDU atstep 1050. In the MBMS subframe corresponding to the MAC PDU that is notgenerated, transmission is stopped until the next SYNC period starts atstep 1060.

The eNB determines whether the SYNC period expires at step 1055. If allof the MAC PDUs scheduled in the MBMS subframe designated in thecorresponding SYNC period are generated with the exception of the MACPDU which is not generated due to the missed RLC SDU, the procedure goesto step 1060. If there is any MAC PDU to be generated, the eNB returnsthe procedure to step 1010.

Second Embodiment

The second embodiment of the present invention proposes a method andapparatus that is capable of generating MAC PDUs normally with theexception of the MAC PDU corresponding to missed RLC SDUs although morethan one RLC SDUs are missed in series. As described above, the reasonwhy the eNB cannot generate a MAC PDU with more than one RLC SDUs missedin series is because the eNB does not know the sizes of individualmissed RLC SDUs. If the information capable of calculating the size ofeach missed RLC SDU is transmitted along with the RLC SDU, the eNB cangenerate the MAC PDUs normally with the received RLC SDUs even when aseries of multiple RLC SDUs are not received.

The information capable of calculating the size of each missed RLC SDUcan be the previous Octet Count (POC) or the information indicating thesize of the data contained in the payload of the previous SYNC frame.For example, if the information capable of calculating the size of[n+2]^(th) RLC SDU is included in the SYNC frame containing [n+3]^(th)RLC SDU, the eNB can calculates the sizes of the missed RLC SDUs evenwhen the SYNC subframe carrying the [n+1]^(th) RLC SDU and the SYNCframe carry the [n+2]^(th) RLC SDU are not received in series. Adescription is made of a method for calculating the sizes of the missedRLC SDUs in when multiple SYNC frames are missed in series.

FIG. 11 is a diagram illustrating the second embodiment of the presentinvention.

Referring to FIG. 11, the current SYNC frame includes the OC of theprevious SYNC frame, and reference numbers 1105 and 1120 denotes theinformation contained in each SYNC frame. Particularly, it is assumedthat the information 1105 to 1120 of the current frame include OCs ofthe previous SYNC frame.

Here, if RLC SDU [n] and RLC SDU [n+3] are received and RLC SDU [n+1]and RLC SDU [n+2] are not received, the size of the RLC SDU [n+2] isobtained by subtracting OC(y3) of RLC SDU [n+2] from OC(y4) of RLC SDU[n+3] such that it is possible to calculates the size (y4−y3) of RLC SDU[n+2] only with the information contained in RLC SDU [n+3]. Likewise,the size of RLC SDU [n+1] is the value obtained by subtracting OC(y2) ofRLC SDU [n+1] from OC(y3) of RLC SDU [n+2].

If the data size (PPS) contained in the payload of the previous SYNCframe, i.e. the RLC SDU size, is transmitted in the SYNC frame asdenoted by reference numbers 1125 and 1140, the size of RLC SDU [n+2] isPPS(z4) of RLC SDU [n+3].

In this case, OC of RLC SDU [n+1] is the value obtained by adding thesize of RLC SDU [n] to OC of RLC SDU [n] such that it is possible tocalculate the size of RLC SDU [n+1] only with the information containedn RLC SDU [n] and RLC SDU [n+3]. That is, the size of RLC SDU [n+1] isobtained by subtracting the size of RLC SDU [n+2] from the sum of theRLC SDU [n+1] and RLC SDU [n+2], i.e. the value obtained by adding theOC of RLC SDU [n+1] and the size of RLC SDU [n+1] to the OC of RLC SDU[n+3].

As described above, if the SYNC frame includes POC or PPS of n SYNCframes, it is possible to calculate the sizes of the missed RLC SDUseven when up to [n+1] SYNC frames are not missed in series.

In case that m RLC SDUs from RLC SDU [n+1] to RLC SDU [n+m] are missedin series, the method for calculating the sizes of the missed RLC SDUsusing POC can be generalized as follows. Here, OC_[x] denotes the 00 ofx^(th) RLC SDU, and rlc sdu size_[x] denotes the size of x^(th) RLC SDU.

Assuming the SYNC frame carrying RLC SDU [n+m+1] includes OCs ofprevious [m−1] RLC SDUs, i.e. OC_[n+2] to OC_[n+m], it can be summarizedas shown in table 1.

TABLE 1 Size of RLC SDU [n + m] = OC_[n + m + 1] − OC_[n + m] Size ofRLC SDU [n + m + 1] = OC_[n + m] − OC_[n + m − 1] . . . Size of RLC SDU[n + 2] = OC_[n + 3] − OC_[n + 2] Size of RLC SDU [n + 1] = sum ofmissed RLC SDUs' sizes − (OC_[n + m + 1] − OC_[n + 2]) Sum of missed RLCSDU's sizes = OC_[n + m + 1] − OC_[n] + rlc sdu size_[n]

In table 1, OC_[n+m+1]−OC_[n+2] is the sum of the sizes of all RLC SDUsfrom RLC SDU [n+2] to RLC SDU [n+m].

Assuming that the SYNC frame carrying RLC SDU [n+m+1] includes theprevious [m−1] RLC SDUs, i.e. rlc sdu size_[n+2]˜rlc sdu size_[n+m], thesize of RLC SDU can be summarized as shown in table 2.

TABLE 2 Size of RLC SDU [n + m] = rlc sdu size_[n + m] Size of RLC SDU[n + m − 1] = rlc sdu size_[n + m − 1] . . . Size of RLC SDU [n + 2] =rlc sdu size_[n + 2] Size of RLC SDU [n + 1] = sum of missed RLC SDUs'sizes − sum of all RLC SDUs from RLC SDU [n + 2] to RLC SDU [n + m]

FIG. 12 is a diagram illustrating a configuration of SYNC frameaccording to the second embodiment of the present invention.

Referring to FIG. 12, the SYNC frame 1205 contains the information of PNand OC 1210 and RLC SDU 1220 like the conventional SYNC frame. Also, theSYNC frame includes the information necessary for the calculation of thesizes of previous RLC SDUs, and this information includes the OCscarried in the previous n SYNC frames or the sizes of the payloads ofthe previous n SYNC frames in sequence.

If the OC values of the n previous SYNC frames or the sizes of the dataof the payloads of the n previous SYNC frames are included in a certainRLC SDU, the eNB can calculate the sizes of [n+1] RLC SDUs carried inthe [n+1] SYNC frames even though [n+1] SYNC frames are missed in seriesright before a certain RLC SDU.

The number of POCs or PPSs that can be carried in the information forcalculating the sizes of previous RLC SDUs influences the link stabilitybetween MBMS server and eNB. For example, if the link is good enough andthus the packet reception error rate is very low, there is littlepossibility to fail receiving two or more RLC SDUs in series. In thiscase, it is possible to prepare for the two missed SYNC frames byincluding one previous POC or PSS in the information for calculating thesizes of the previous RLC SDUs. If the link state is unstable, it ispossible to prepare for a plurality of SYNC frames missed in series byincluding POCs or PSSs as many as possible.

The number of POCs or PSSs to be contained in the SYNC frame can beagreed as a predetermined value between MBMS server and eNBs andadjusted, if necessary, by the MBMS server. For example, the MBMS servercan transmit one POC or PSS in normal state but multiple POCs or PSSs iflink condition is degraded.

FIG. 13 is flowchart illustrating an eNB procedure according to thesecond embodiment of the present invention.

Referring to FIG. 13, if a certain SYNC period starts at step 1305, theeNB starts operation for configuring MAC PDU to be transmitted in thefirst MBMS subframe for which no MAC PDU is configured among the MBMSsubframes designated in the SYNC period at step 1310. That is, the eNBsegments or concatenates the RLC SDUs that are not included in any MACPDU yet or some of the RLC SDUs in match with the RLC PDU size to beencapsulated in the MAC PDU.

At this time, the eNB monitors to determine whether a missed RLC SDU isdetected until the payload of RLC PDU is filled entirely at step 1315and, if the payload of the RLC PDU is filled without missed RLC SDU, theprocedure goes to step 1320 and, otherwise if any missed RLC SDU isdetected until the payload of RLC PDU is filled entirely, step 1330.

At step 1320, the eNB adds a header to the RLC payload generated bysegmenting/concatenating RLC SDUs to generate RLC PDUs and multiplexesthe RLC PDUs into MAC PDU. Next, the eNB transmits the MAC PDU in thecorresponding MBMS subframe at step 1325, and the procedure goes to step1355.

If any missed RLC SDU is detected before the payload of the RLC PDU isfilled entirely at step 1315, the procedure goes to step 1330. At step1330, the eNB determines whether it is possible to calculate the sizesof all missed RLC SDUs. Under the assumption that the number of RLC SDUsmissed in series is n and the number of POCs or PSSs contained in theSYNC frame following the last missed RLC SDU is m, if n is greater thanm+1, the eNB cannot calculate the sizes of some of the missed RLC SDUs;and otherwise if n is equal to or less than m+1, the eNB can calculatethe sizes of all missed RLC SDUs. If it is possible to calculate thesizes of all missed RLC SDUs, the procedure goes to step 1335 and,otherwise if it is possible to calculate the sizes of some of the missedRLC SDUs, step 1350.

At step 1335, the eNB determines the MAC PDU corresponding to the MBMSsubframe in which the missed RLC SDU is scheduled in consideration ofthe size of the missed RLC SDU. This can be done through a normal MACPDU generation process by generating a virtual RLC SDU having the samesize as the missed RLC SDU and determining the MAC PDU in which the RLCSDU having the same size as the missed RLC SDU is to be contained. TheneNB suspends transmission in the MBMS subframe corresponding to the MACPDU in which the missed RLC SDU is to be transmitted at step 1340, andthe procedure goes to step 1345.

Next, the eNB transmits the first MAC PDU generated with the valid RLCSDUs in the corresponding MBMS subframe at step 1345. This can be doneby generating a virtual RLC SDU having the same size as the missed RLCSDU and continuing the normal MAC PDU generation process until the firstMAC PDU in which the RLC SDU having the same size as the missed RLC isnot contained.

If it is impossible to calculated the sizes of some missed RLC SDUs atstep 1330, the procedure goes to step 1350. At step 1350, the eNBtransmits the MAC PDUs generated until then in the corresponding MBMSsubframe and stops generating MAC PDU anymore. The transmission stops inthe MBMS subframe corresponding to the non-generated MAC PDUs, and theprocedure goes to step 1360.

The eNB determines whether the SYNC period has expired at step 1355. Ifall of the MAC PDUs to be transmitted in the MBMS subframe during thecorresponding SYNC period are generated with the exception of the MACPDUs excluded by the missed RLC SDUs, the procedure goes to step 1360.If there is MAC PDUs that are not generated yet, the eNB returns theprocedure to step 1310.

Third Embodiment

In the third embodiment of the present invention, the MBMS servertransmits a control message including the information on the size of thepayload of each synch frame in a SYNC period to the eNB. If the controlmessage is received, the eNB can checks the sizes of all RLC SDUs in thecorresponding SYNC period so as to generate the MAC PDUs correspondingto the received RLC SDUs successfully regardless of the number of missedSYNC frames.

FIG. 14 is a drawing illustrating the third embodiment of the presentinvention.

Referring to FIG. 14, the MBMS server 1410 transmits n SYNC frames fromthe SYNC frame 1415 having PN of 0 to the SYNC frame 1425 having PN of nwhich contain RLC SDUs to the eNB 1405 in the SYNC period x. the MBMSserver also transmits a control message 1430 informing of the sizes ofpayloads of the SYNC frames or the sizes of contained RLC SDUs to theeNB 1405 for the SYNC period x.

The control message 1430 contains the sizes of the RLC SDUs carried inthe SYNC frame for the SYNC period x. For example, the sizes of all RLCSDUs contained in the SYNC frames for the SYNC period x, e.g. the sizeof RLC SDU [0] contained in the SYNC frame [0] and the size of RLC SDU[1] contained in the SYNC frame [1], can be included.

In case that the control message 1430 informing of the sizes of RLC SDUsis transmitted separately, there is no need to transmit the OCinformation in the SYNC frames such that the OC information is notincluded in the headers of the SYNC frames carrying the RLC SDUs in thetheir embodiment of the present invention. Accordingly, the eNB whichhas not received the control message indicating the sizes of RLC SDUscannot generate the MAC PDUs precisely after failing receipt of any RLCSDU even when only one RLC SDU is not received and, as a consequence,stop transmission in the MBMS subframe until the next SYNC periodstarts.

If the control message 1430 indicating the sizes of RLC SDUs is receivedsuccessfully, the eNB can generate MAC PDUs with the successfullyreceived RLC SDUs even through some RLC SDUs are not received andtransmit the generated MAC PDUs in the MBMS subframe with the exceptionof the MAC PDUs corresponding to the missed RLC PDUs.

FIG. 15 is a flowchart illustrating an eNB device operation according tothe third embodiment of the present invention.

Referring to FIG. 15, if a SYNC period starts at step 1505, the eNBconfigures the MAC to be transmitted in the first MBMS subframe forwhich not MAC PDU is configured yet among the MBMS subframes in the SYNCperiod at step 1510. The eNB segments or concatenates, in series, theRLC SDUs not included in any MAC PDU yet or some of RLC SDUs, in matchwith the size of RLC SDU to be encapsulated in the MAC PDU.

At this time, the eNB monitors to determine whether any missed RLC SDUis detected until the payload of RLC PDU is filled entirely at step 1515and, if the payload of the RLC PDU is filled without missed RLC SDU, theprocedure goes to step 1520 and, otherwise if any missed RLC SDU isdetected until the payload of RLC PDU is filled entirely, step 1530.

At step 1520, the eNB adds a header to the RLC payload generated bysegmenting/concatenating RLC SDUs to generate RLC PDUs and multiplexesthe RLC PDUs into MAC PDU. Next, the eNB transmits the MAC PDU in thecorresponding MBMS subframe at step 1525, and the procedure goes to step1555. If any missed RLC SDU is detected before the payload of the RLCPDU is filled entirely at step 1515, the procedure goes to step 1530.

At step 1530, the eNB determines whether a control message including theinformation on the sizes of the RLC SDUs for the SYNC period isavailable. If the control message is available, the procedure goes tostep 1535 and, otherwise, step 1550.

At step 1535, the eNB checks the sizes of the missed RLC SDUs using theinformation contained in the control message and determines the MAC PDUcorresponding to a MBMS subframe in which the missed RLC SDU isencapsulated in consideration of the sizes of the missed RLC SDUs. Thiscan be done by generating a virtual RLC SDU having the same size as themissed RLC SDU and continuing the normal MAC PDU generation process soas to check the MAC PDU in which the RLC SDU is encapsulated therein.Next, the eNB stops transmission in the MBMS subframe corresponding tothe MAC PDU reserved to carry the missed RLC SDU, and the procedure goesto step 1545.

Next, the eNB configures the first MAC PDU with the valid RLC SDUs andtransmits the first MAC PDU in the corresponding MBMS subframe. This canbe done by generating a virtual RLC SDU having the same size as themissed RLC SDU and continuing the normal MAC PDU generation processuntil the first MAC PDU in which the RLC SDU having the same size as themissed RLC is not contained.

It the control message informing of the sizes of the RLC SDUs is notavailable at step 1530, the procedure goes to step 1550. At step 1550,the eNB transmits the MAC PDUs generated until then in the correspondingMBMS subframe and stops generating MAC PDU anymore. The transmissionstops in the MBMS subframe corresponding to the non-generated MAC PDUs,and the procedure goes to step 1560.

The eNB determines whether the SYNC period has expired at step 1555. Ifall of the MAC PDUs to be transmitted in the MBMS subframe during thecorresponding SYNC period are generated with the exception of the MACPDUs excluded by the missed RLC SDUs, the procedure goes to step 1560.If there is any MAC PDU that is not generated yet, the eNB returns theprocedure to step 1510.

FIG. 16 is a block diagram illustrating the eNB device according to anembodiment of the present invention.

Referring to FIG. 16, an L1 reception device 1605 is the device forreceiving the data transmitted by the MBMS server. According to the typeof the wired link connected to the eNB, the L1 reception device 1605 canbe an Ethernet reception device or an optical reception device. The datareceived by the L1 reception device 1605 are input to the demultiplexingdevice 1607. The demultiplexing device 1607 transfers the SYNC framecorresponding to a certain MBMS service to the SYNC frame processor ofthe corresponding MBMS service.

The SYNC frame processor 1615 receives the SYNC frame and transfers theRLC SDU contained in the payload and related information, e.g. PN andOC, to the RLC SDU storage 1620. The SYNC frame processor 1615 transfersPOC or PPS carried in the SYNC frame to a missed RLC SDU size calculator1610. If the control message including the RLC SDU size information isreceived, the SYNC frame processor 1615 also transfers the controlinformation to the missed RLC SDU size calculator 1610.

The RLC SDU storage 1620 stores all or some of RLC SDUs that are nottransmitted in sequence of PNs. If the PNs of two adjacent RLC SDUs arenot consecutive, the RLC SDU storage 1620 transfers the non-consecutivePNs and OCs corresponding to the PNs to the RLC SDU size calculator1610. Afterward, the RLC PDU payload generation process is performed inconsideration of the sizes of the missed RLC SDUs that are notified bythe missed RLC SDU size calculator 1610. The RLC SDU storage 1620segments/concatenates all or some of the RLC SDUs in match with the sizerequired in the RLC PDU generator 1625 to generate the RLC PDU payloadand transfers the RLC PDU payload to the RLC PDU generator 1625.

If the RLC PDU payload is not filled entirely due to the missed RLCSDUs, the RLC SDU storage 1620 notifies the RLC PDU generator 1625 thatthere is no data to provide. If the missed RLC SDU size calculator 1610notifies the RLC SDU storage 1620 that the missed SDU size calculationis impossible after a specific RLC SDU, the RLC SDU storage 1620 stopsgenerating RLC payload with the RLC SDU from the specific RLC SDUanymore and notifies the RLC PDU generator 1625 that there is not datato be provided. Otherwise if the missed RLC SDU size calculator 1610notifies the RLC SDU storage 1620 of the sizes of the missed RLC SDUs,the RLC SDU storage 1620 generates the RLC PDU payload from the timepoint when the RLC PDU payload generation is possible in considerationof the sizes of the missed RLC SDUs and transfers the RLC PDU payload tothe RLC PDU generator 1625.

The missed RLC SDU size calculator 1610 calculates the sizes of themissed RLC SDUs based on the information provided by the SYNC frameprocessor 1615 and RLC SDU storage 1620 and transfers this informationto the RLC SDU storage 1620. The missed RLC SDU size calculator 1610also notifies the RLC SDU storage 1620 that the sizes of the missed RLCSDUs cannot be calculated.

The RLC PDU generator 1625 generates RLC PDU in size indicated by thetransmission controller 1653. The RLC PDU generator 1625 determines theamount of data to be contained in the RLC PDU payload in match with thesize indicated by the transmission controller 1653 and instructs the RLCSDU storage 1625 to generate the payload in corresponding size. The RLCPDU generator 1625 generates RLC PDU by adding an RLC header to thepayload provided by the RLC SDU storage 1620 and transfers the RLC PDUto the MAC PDU generator 1630. If there is no RLC PDU payload providedfrom the RLC SDU storage 1620, the RLC PDU generator 1625 also does notprovide RLC PDU to the MAC PDU generator 1630.

The MAC PDU generator 1630 encapsulates the RLC PDU provided by the RLCPDU generator 1625 as payload and adds a MAC header to generate a MACPDU. The MAC PDU generator 1630 transfers the MAC PDU to the L1transmission device 1640 at the time point indicated by transmissioncontroller 1635. If nor RLC PDU is provided by the RLC PDU generator1625, the MAC PDU generator 1630 cannot generate MAC PDU.

The L1 transmission device 1640 transmits the MAC PDU provided by theMAC PDU generator 1630 at the transmission time point indicated by thetransmission controller 1635 on the predetermined transmission resourceaccording a predetermined modulation/channel coding scheme. If there isno MAC PDU provided by the MAC PDU generator 1630 at the time pointindicated by the transmission controller 1635, the L1 transmissiondevice 1640 does not start transmission at the transmission time point.

The transmission controller 1635 checks the MBMS subframe and controlsthe RLC PDU generator 1625, MAC PDU generator 1630, and L1 transmissiondevice 1640 to transmit MAC PDUs in the MBMS subframe at an appropriatetime point before the start of the MBMS subframe.

As described above, the method and apparatus for transmitting multimediabroadcast data in a wireless communication system according to thepresent invention is capable of transmit data stably while maintainingdata integrity of the multimedia broadcast data.

While the present invention has been particularly shown and describedwith reference to certain embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims and theirequivalents.

What is claimed is:
 1. A method by a base station in a wirelesscommunication system, the method comprising: receiving a plurality ofservice data unit (SDUs) from a core network node; receiving a controlmessage including a plurality of length information respectivelycorresponding to the plurality of SDUs from the core network node;identifying a loss of at least one SDU; determining a subframe impactedby the loss of the at least one SDU, based on the length information inthe control message; and muting the determined subframe, wherein theplurality of SDUs and the control message are received separately. 2.The method of claim 1, further comprising: generating a MAC protocoldata unit (PDU) encapsulating valid SDUs; and transmitting the MAC PDUencapsulating the valid SDUs in a corresponding multimedia broadcastmulticast service (MBMS) subframe.
 3. The method of claim 1, furthercomprising processing the plurality of SDUs using the lengthinformation.
 4. The method of claim 1, wherein the length informationincluded in the control message is used, when consecutive SDUs are lost.5. The method of claim 1, further comprising: identifying at least twoconsecutive, lost SDUs; determining a subframe impacted by the at leasttwo consecutive, lost SDUs using the length information in the controlmessage; and muting the determined subframe impacted by the at least twoconsecutive, lost SDUs.
 6. The method of claim 1, wherein the controlmessage further includes respective length information of other SDUstransmitted from the core network node in a synchronization period. 7.The method of claim 1, wherein the length information is received at anend of a synchronization period of the plurality of SDUs.
 8. A basestation in a wireless communication system, the base station comprising:a transceiver configured to transmit and receive a signal; and acontroller configured: to receive a plurality of service data unit(SDUs) from a core network node, to receive a control message includinga plurality of length information respectively corresponding to theplurality of SDUs from the core network node, to identify a loss of atleast one SDU, to determine a subframe impacted by the loss of the atleast one SDU, based on the length information in the control message,and to mute the determined subframe, wherein the plurality of SDUs andthe control message are received separately.
 9. The base station ofclaim 8, wherein the controller is further configured: to generate a MACprotocol data unit (PDU) encapsulating valid SDUs, and to transmit theMAC PDU encapsulating the valid SDUs in a corresponding multimediabroadcast multicast service (MBMS) subframe.
 10. The base station ofclaim 8, wherein the controller is further configured to process theplurality of SDUs using the length information.
 11. The base station ofclaim 8, wherein the controller is further configured to mute theplurality of SDUs, when consecutive SDUs are lost, using the lengthinformation included in the control message.
 12. The base station ofclaim 8, wherein the controller is further configured: to identify atleast two consecutive, lost SDUs, to determine a subframe impacted bythe at least two consecutive, lost SDUs using the length information inthe control message, and to the determined subframe impacted by the atleast two consecutive, lost SDUs.
 13. The base station of claim 8,wherein the control message further includes respective lengthinformation of other SDUs transmitted from the core network node in asynchronization period.
 14. The base station of claim 8, wherein thelength information is received at an end of a synchronization period ofthe plurality of SDUs.